Previous studies have clearly established the presence of peptide-containing amacrine cells in all vertebrate retinas. These identified amacrine cells belong to limited, morphologically distinct populations. The long term objective of these studies is to define the anatomical organization of the inner plexiform layer (IPL) in order to gain a better understanding of visual processing. This will be accomplished by using the peptide-like immunoreactivity of amacrine cells as a means to defining A) amacrine cell morphology and spatial organization, B) the ultrastructure and synaptic relationships, C) the circuitry of amacrine cells in relationship to other identified bipolar and ganglion cells and D) the ontogeny of amacrine cells. These studies will utilize immunohistochemical techniques in both sectioned and whole mount preparations of avian and rabbit retina. An important aim of the proposed studies is to define the histochemical organization of local IPL circuits that are associated with histochemically defined bipolar cells and specific horseradish peroxidase-wheat germ agglutinin (HRP-WGA) retrogradely labeled ganglion cells. Studies examining local IPL circuitry will use double label immunohistochemistry with autoradiography or horseradish peroxidase histochemistry. These studies will define amacrine cell morphology, IPL circuitry and provide information about the role of peptides in the retina. The ultimate goal of these studies is to provide a basis for understanding the structural and histochemical organization of the retina in order to understand visual processing and to aid in diagnosis and treatment of retinal and choroidal diseases.